This invention relates to a vent system for an electric storage battery, and more specifically to a vent system with a flame arresting system having means for preventing the transmission of a flame through the vent system and into the battery and means for extinguishing the flame before it reaches the inside of the battery.
In reading the following disclosure, it should be noted that the invention disclosed and claimed herein, and the discussion concerning it, are applicable to many kinds of battery systems, and that the references to applications in the area of automotive batteries and maintenance free automotive batteries are made to illustrate possible uses of the invention, and not for the purpose of limiting the scope of the claimed invention.
The chemical reactions which take place within batteries can produce explosive gases, which are usually relieved through a vent system. In the event a spark should occur in the area of the battery vent plugs, such as when a connection is made to the battery, the gases being emitted from the battery can be easily ignited. One time when this situation occurs is when a battery is being charged or is being overcharged. Should the flame travel through the vent system, the battery itself would explode.
Several prior art systems have addressed this problem. A few systems use apertures through which the gases escape, which are small enough to prevent the flame from entering the vent plug. Other systems utilize restricted passageways formed inside the vent plug, which are not large enough to permit combustion or the transmission of a flame. Still other systems use porous diffusors or other similar devices which function in a manner similar to a fire screen. While these systems may extinguish a flame adequately, if one occurs, permanent damage may be done to the vent plug, thereby impairing their effectiveness or even requiring its replacement.
Another trend in solving the explosion prevention problem has been to create a chamber wherein a controlled explosion will take place in the event the gases expelled through the vent plug are ignited. One such example is U.S. Pat. No. 3,879,227, issued to Hennen, wherein a porous diffuser prevents passage of the flame through the vent plug so that a controlled explosion takes place in the explosion chamber immediately outside the porous diffuser, thereby extinguishing the flame. Potential problems when using a ceramic porous diffuser include increased costs and risks that the diffuser will eventually clog up.
When designing a vent system for use with an automotive maintenance free battery, other considerations are important. An automotive maintenance free battery is designed so that throughout its normal life, no attention is required by the user, such as the addition of water to the individual cells. As a result, most manufacturers have the liquid level of the electrolyte as high as practically possible, without interferring with the venting operations, so as to provide an adequate reserve of electrolyte throughout the life of the battery. In an effort to maximize the liquid level for a given battery, the vent plugs should be made so that the distance they extend into the vent well is minimized. This problem is complicated further since marketing considerations often require the single vent plug to be flush with the top of the battery cover, so as to provide a "maintenance free" look.